This invention relates to the securing of anchor bolts in drilled openings in a mine roof for supporting the roof.
For many years, mine roof bolts of the expansion shell type have been widely used for supporting mine roofs. More recently, resin type anchors have been employed. In the resin type anchor, a resin and catalyst cartridge is inserted into the back of a mine roof opening, following which an anchor bolt is forced upwardly into the opening, thereby rupturing the cartridge to permit the resin and catalyst to gravitate downwardly between the bolt and the wall of the opening. Upon mixing of the catalyst and the resin, the resin sets to secure the bolt in the mine roof.
Difficulty has been experienced in properly mixing the resin and catalyst to effect the greatest securing effect, and preventing either undermixing or overmixing of the resin and catalyst. Attempts have been made to provide a combination anchor of the present type wherein anchoring of the bolt is carried out by means of an expansion shell acting in combination with resin, as illustrated in U.S. Pat. No. 3,702,060 issued Nov. 7, 1972, U.S. Pat. No. 4,160,614 issued July 10, 1979 and U.S. Pat. No. 4,194,858 issued Mar. 25, 1980. Additionally, U.S. Pat. No. 3,188,815 issued June 15, 1965 discloses an anchor bolt assembly wherein a resin and catalyst cartridge is punctured by the tip of the roof bolt, following which the bolt is rotated a certain number of times in order to mix the resin and catalyst, following which an expansion shell carried by the bolt is urged to its expanded position to grip the mine roof.
It is found, however, that with all of the above combination anchors, proper mixing of the resin and catalyst is a problem, and overmixing or undermixing of the resin occurs, with a consequent reduction in the effectiveness of the resin in securing the bolt in the mine roof opening.